/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.coprocessor;

import java.io.IOException;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;

import org.apache.hbase.thirdparty.com.google.protobuf.Message;

/**
 * Defines how value for specific column is interpreted and provides utility methods like compare,
 * add, multiply etc for them. Takes column family, column qualifier and return the cell value. Its
 * concrete implementation should handle null case gracefully. Refer to
 * {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter} for an example.
 * <p>
 * Takes two generic parameters and three Message parameters. The cell value type of the interpreter
 * is &lt;T&gt;. During some computations like sum, average, the return type can be different than
 * the cell value data type, for eg, sum of int cell values might overflow in case of a int result,
 * we should use Long for its result. Therefore, this class mandates to use a different (promoted)
 * data type for result of these computations &lt;S&gt;. All computations are performed on the
 * promoted data type &lt;S&gt;. There is a conversion method
 * {@link ColumnInterpreter#castToReturnType(Object)} which takes a &lt;T&gt; type and returns a
 * &lt;S&gt; type. The AggregateIm&gt;lementation uses PB messages to initialize the user's
 * ColumnInterpreter implementation, and for sending the responses back to AggregationClient.
 * <p>
 * &lt;T&gt; Cell value data type<br>
 * &lt;S&gt; Promoted data type<br>
 * &lt;P&gt; PB message that is used to transport initializer specific bytes<br>
 * &lt;Q&gt; PB message that is used to transport Cell (&lt;T&gt;) instance<br>
 * &lt;R&gt; PB message that is used to transport Promoted (&lt;S&gt;) instance
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public abstract class ColumnInterpreter<T, S, P extends Message, Q extends Message,
  R extends Message> {

  /**
   * nnn * @return value of type T n
   */
  public abstract T getValue(byte[] colFamily, byte[] colQualifier, Cell c) throws IOException;

  /**
   * nn * @return sum or non null value among (if either of them is null); otherwise returns a null.
   */
  public abstract S add(S l1, S l2);

  /**
   * returns the maximum value for this type T n
   */

  public abstract T getMaxValue();

  public abstract T getMinValue();

  /**
   * nnn
   */
  public abstract S multiply(S o1, S o2);

  /**
   * nn
   */
  public abstract S increment(S o);

  /**
   * provides casting opportunity between the data types. nn
   */
  public abstract S castToReturnType(T o);

  /**
   * This takes care if either of arguments are null. returns 0 if they are equal or both are null;
   * <ul>
   * <li>&gt; 0 if l1 &gt; l2 or l1 is not null and l2 is null.</li>
   * <li>&lt; 0 if l1 &lt; l2 or l1 is null and l2 is not null.</li>
   * </ul>
   */
  public abstract int compare(final T l1, final T l2);

  /**
   * used for computing average of &lt;S&gt; data values. Not providing the divide method that takes
   * two &lt;S&gt; values as it is not needed as of now. nnn
   */
  public abstract double divideForAvg(S o, Long l);

  /**
   * This method should return any additional data that is needed on the server side to construct
   * the ColumnInterpreter. The server will pass this to the {@link #initialize} method. If there is
   * no ColumnInterpreter specific data (for e.g.,
   * {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter}) then null should be
   * returned.
   * @return the PB message
   */
  public abstract P getRequestData();

  /**
   * This method should initialize any field(s) of the ColumnInterpreter with a parsing of the
   * passed message bytes (used on the server side). n
   */
  public abstract void initialize(P msg);

  /**
   * This method gets the PB message corresponding to the cell type n * @return the PB message for
   * the cell-type instance
   */
  public abstract Q getProtoForCellType(T t);

  /**
   * This method gets the PB message corresponding to the cell type n * @return the cell-type
   * instance from the PB message
   */
  public abstract T getCellValueFromProto(Q q);

  /**
   * This method gets the PB message corresponding to the promoted type n * @return the PB message
   * for the promoted-type instance
   */
  public abstract R getProtoForPromotedType(S s);

  /**
   * This method gets the promoted type from the proto message n * @return the promoted-type
   * instance from the PB message
   */
  public abstract S getPromotedValueFromProto(R r);

  /**
   * The response message comes as type S. This will convert/cast it to T. In some sense, performs
   * the opposite of {@link #castToReturnType(Object)} nn
   */
  public abstract T castToCellType(S response);
}
